Sinister Cannibals or Nurturing Fathers?

In majority of sexually reproducing species females are the choosy ones. Generally, females invest more in offspring during pregnancy and post-natal care. Males try many tricks (fighting with other males, making elaborate dances, providing nuptial gifts, carrying showy and difficult to maintain body ornaments etc.) to prevent being filtered out in female preferences. Parental investment is a determinant in choosiness. In this post we will take a look at a spectrum of male behavior in parental care. Pipefishes and mudskippers are at the extreme ends of this spectrum while bluegill sunfishes are in between.

Pipefishes (Syngnathus spp.) are very close relatives of seahorses. In these fishes the sexual roles that we are accustomed to see in nature are reversed. Males invest more on offspring. Size matters a lot in aquatic environments. Male pipefishes prefer mating with larger females. Larger females bear larger eggs having higher survival capacity. After mating male pipefish take over the fertilized eggs and rears the brood in his pouch for 12 to 14 days. This is what is happening in the video above. Two female ghost pipefishes Solenostomus cyanopterus are competing to get their eggs fertilized by the larger male. While each one is trying to have access to the male she is also trying to keep the other away. It is pretty noticeable that females have two color morphs.

A study by Kimberly Paczolt and Adam Jones from Texas A&M University has revealed a rather sinister turn of events. Pregnancy depletes male resources rapidly especially after mating with a large female with energetically demanding large eggs. After such a pregnancy males can mate with smaller females and instead of rearing the eggs they digest them. In this way they recover faster for another round of pregnancy. Cannibals!

Bluegill sunfishes have a well-documented intermediate behavior. In these fishes males prepare and defend the nest. Males only allow females to approach and lay eggs and chase away other males. They also fan the eggs with their fins to oxygenate so that the brood develop faster. During this period (can be up to 10 days) they can’t feed themselves and can lose 10 percent of their body weight. There are however certain small satellite males who mimic females. Genetic studies have shown that these impostors can sneak into the nest and fertilize the eggs. The video below is an outstanding work showing snapshots of nesting behavior in longear sunfish Lepomis megalotis.

Starting from 20 seconds into the video, you can see a satellite male making several attempts to fertilize the eggs. This is when the story gets interesting. Satellite males parasitize the nest and get their offspring guarded by the resident male. This is a very useful strategy with no parental investment. On the other hand resident males seem to have an equally sinister counter strategy. Once the fish fry begin to hatch resident males cannibalize on a fraction of them. Scientists were rather curious whether the resident males could differentiate hatchlings sired by satellite males. This ability has been shown in a central American fish Midas cihclids using controlled aquarium experiments. Genetic analysis on darters and sunfishes have shown that sunfishes can’t. If they could it would be an intriguing story where resident males perhaps intentionally turned a blind eye to satellites in order to consume their hatchlings. In this evolutionarily stable strategy males are cannibalistic.

There’s hope however: Mudskippers (Periophthalmus argentilineatus). Even though they are not lobe-finned which are the ancestors of tetrapods (vertebrate animals that first colonized land) these ray-finned fishes help us greatly for understanding locomotion in this key evolutionary step that took place between 380-360 million years ago. Mudskippers are the inspiring role models demonstrating that there are indeed completely altruistic fathers in nature who devote themselves to their babies.



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